A variety of chemical, immunochemical metabolic and biochemical analyses will be applied to studies of parathyroid hormone, calcitonin and vitamin D in humans and animals. Studies of the isolation, sequence analysis and synthesis of the peptide hormones will be coupled with analysis of the biosynthesis, secretion and metabolism of parathyroid hormone and calcitonin. Particular interest centers on pro-parathyoid hormone and a larger precursor, pre-proparathyroid hormone, as well as the messenger RNA and complementary DNA, reflecting respectively the initial product of gene translation, the ribosomal active species, and the functionally active gene. The production, metabolic transformation and blood transport of vitamin D will be assessed in relation to calcium homeostasis. Particular attention is directed to the photobiology of vitamin D production in skin. Radioactive vitamin D metabolites, including 1,25-(OH)2D3, have been prepared and will be applied to analysis of the control of photobiology metabolism, transport and mode of action of vitamin D. The mode of parathyroid hormone action will be studied at the cellular and biochemical level with particular emphasis on interaction of the hormones with their bioreceptors in target cells in kidney and bone. Specific clinical application through improved assays for parathyroid hormone, calcitonin and vitamin D will be made to the diagnosis and treatment of hyperparathyroidism, medullary carcinoma of the thyroid, calcium and vitamin D deficiency states, osteomalacia, Paget's disease of bone and hypocalcemic disorders.